Contact-free display peripheral device for contact-free portable object

ABSTRACT

A peripheral display device for a portable contactless object such as a smart card ( 10 ) enabling information associated with the use of this portable object to be displayed. This peripheral device includes at least one chip, a display ( 16 ) and a receiver for receiving energy and information ( 18 ), not connected by an ohmic contact to the portable object. This receiver is a flat coil which plays the role of the secondary of a transformer, the primary of which is formed by the antenna ( 14 ) of the portable object, when the latter receives energy and information from a portable object reader via electromagnetic coupling.

This application is a U.S. National Stage of International ApplicationPCT/FR01/02010, filed Jun. 26, 2001 and published on Jan. 3, 2002 in theFrench Language.

TECHNICAL FIELD

The present invention concerns peripheral objects for portablecontactless objects such as smart cards, and particularly a contactlessperipheral display device.

BACKGROUND ART

Portable objects, such as smart cards, contact or contactless type, arecurrently widely used in numerous applications. It generally entails ISOformat cards which are coupled to readers, by which they are remotelysupplied, that is, by which they receive energy in the form of amagnetic field and with which they communicate. In the transport sector,such systems, called remote toll cards, have been developed by all ofmotorway operators in order to provide users with subscriptionpossibilities and to simplify toll booth payment operations. Users ofsuch systems present the cards in front of readers which are installedin the toll booths. Communication thus occurs between the card and thereader. This communication enables user recognition and thecorresponding sum to be deducted from the customer's account at the tollbooth.

In public transport sectors, equivalent means have also be implementedin the form of ISO cards or in a smaller format such as tickets. Userspresent the subscription cards in front of readers in order to gainaccess to public transport. The communication which is establishedbetween the card and the reader enables user recognition and the cost ofthe trip to be deducted from the user's account.

These means have also been developed as a means of payment. This is thecase, for example, of the electronic wallet. The latter can be used topay for small purchases in shops. It consists of a smart card. This cardis credited with money in a special distributor. The user may thus usethe card to pay for purchases by presenting it in front of a reader. Thecommunication established between the card and the reader debits the sumcorresponding to the purchase from the card.

Many companies has also developed identification means for theirpersonnel using contactless smart cards. Passing the card in front of areader allows the cardholder to be identified, who is then granted orrefused access to a controlled zone. The same card can also be used byemployees to “punch in”.

These various applications have given rise to the need of a peripheraldisplay device on the card, enabling the user to retrieve theinformation contained in the chip, such as the available balanceremaining after a transaction in the case of an electronic wallet or thenumber of trips still available on a transport card or even the numberof hours worked, or the authorization or refusal to access areasreserved for the employees of a company. Such a peripheral device mayalso be used to supply the user with more technical information aboutthe card's operation.

The solution commonly used is the integration of a liquid crystaldisplay in the reader which informs the user that communication has beenproperly established and displays the information related to thecommunication. However, the drawback of having a display unit built intothe reader is that the user can gain access to the information bypassing the card in front of the reader. While this is not a problem inthe case of an identification card, it becomes much more problematic inthe case of an electric wallet or transport card. The user would like tobe able to regularly consult his/her balance without having to find apayment terminal just to read the card.

A solution currently exists which entails the use of an additional badgewhich plays the role of both a card reader and display unit. It is infact a sort of case in which the card is inserted. The reader providespower to the card by direct contact, which enables communication to takeplace between the card and the case. The information is then displayedon the screen of the case. The latter is used particularly forelectronic wallet cards and allows the balance remaining on the card tobe consulted at all times. The major drawback of these badges is theirsize. The cases are dimensioned to receive an ISO smart card. As such,contrary to a smart card, they cannot be carried in a wallet and must becarried in a pocket or purse.

Another drawback is that they require an internal power source. Thispower source is typically a battery which enables the case to read anddisplay the information stored in the card. The power source must thusbe renewed once it is depleted.

DISCLOSURE OF THE INVENTION

The purpose of the invention is to mitigate these drawbacks by supplyinga contactless peripheral display for contactless portable objects, suchas a smart card, having the capacity to display the information sent bythe portable object reader or by the portable object itself, for aperiod of time long enough so that the user can consult it at all times,even when the portable object is not in the proximity of the reader,this display requiring only a small amount of energy to operate, or evenno energy whatsoever.

The present invention concerns a peripheral display device for acontactless portable object such as a smart card enabling informationassociated with the use of this portable object to be displayed. Thisperipheral device includes at least one chip, a display means and ameans for receiving energy and information, not connected by an ohmiccontact to the portable object. This receiving means is a flat coilwhich plays the role of the secondary of a transformer, the primary ofwhich is formed by the antenna of the portable object, when the latterreceives energy and information from a portable object reader viaelectromagnetic coupling.

According to a special embodiment of the invention, this peripheraldisplay device can be separated from the contactless object and featuresa bistable liquid crystal display screen.

BRIEF DESCRIPTION OF THE FIGURES

The purposes, objects and characteristics of the invention will becomemore apparent from the following description when taken in conjunctionwith the accompanying drawings in which:

FIG. 1 represents an ISO format contactless smart card featuring abuilt-in peripheral display device.

FIG. 2 represents a block diagram of the peripheral display device andits various components.

FIG. 3 represents the electrical schematic diagram of a contactlesssmart card.

FIG. 4 represents the circuit diagram of a peripheral display device.

DETAILED DESCRIPTION OF THE INVENTION

The peripheral display device according to the invention may thus beinstalled on a contactless portable object such as a smart card. FIG. 1represents an ISO format contactless smart card featuring a built-inperipheral display device. This card 10 consists of a chip 12. When thecard is placed in the field of the reader, this chip enters intocommunication with the reader by means of the card's antenna 14. Thisantenna consists of turns of increasing circumference. Each of the endsof this antenna is connected to the chip 12. The peripheral displaydevice 20 consists of a chip (not visible in the figure), a screen 16and a flat coil 18 connected to the chip of the peripheral displaydevice and formed by turns of increasing circumference. The size of thisflat coil varies depending on the special characteristics of the cardwith which the peripheral display device operates. The peripheraldisplay device operates only when magnetically coupled to the card, atthe working frequency of the card's chip.

According to FIG. 2, the peripheral display device preferably consistsof a chip 22, connected to the coil 18 and to the screen 16. The chip 22is made up of 3 blocks: the analog block 24, the message decoding block26 and the display block 28.

The role of the analog block 24 is to rectify and regulate thealternating signal, available on the terminals of the coil 18. Thissignal is created by a carrier signal of 13.56 megahertz (MHz), which isthe coupling frequency between the contactless smart card and thereader, to generate the continuous supply voltage required to operatethe peripheral display device. It shapes the main clock signals issuedfrom this carrier frequency of 13.56 MHz, which enables the sequentialoperation of the peripheral display device. It extracts and transformsthe superimposed data according to the amplitude modulation at thecarrier frequency of 13.56 MHz, transmitted by the reader to thecontactless smart card and the peripheral display device. It can modifythe impedance which it presents to the coil 18, by switching aresistance, at a retromodulation subcarrier frequency issued from themain clock, in order to enable the transmission of data from theperipheral display device to the reader, by means of data modulatingthis subcarrier frequency (modulation of the coupling with the antennasdirectly opposite). According to a specific example, the value of theretromodulation subcarrier frequency is equal to 847 kilohertz (kHz)(standard currently used). It can also be configured to receive the datawhich will be transmitted on the retromodulation subcarrier frequency bythe card's chip.

The peripheral device is also equipped with a message decoding block 26.This block is more or less complex. It may be a microcontroller, asimple decoder or even a hardwired logic circuit. This block is designedto separate and process the messages that are sent to it among thosewhich transit via the carrier and subcarrier frequencies duringcommunication between the coupler and the contactless card.

The display control block 28 is an interface circuit allowing the datareceived by the peripheral display device to be converted into signalswhich are compatible with the display technology used, consisting of thescreen 16, in order to drive the corresponding pixels or segments.

As far as the coil 18 of the peripheral device is concerned, itsdimensions are very variable and depend on the consumption and thevoltage required to supply the peripheral device.

Thus, in the case of a peripheral display device having energyconsumption much lower than that of the card's chip, the coil 18 of theperipheral display device will be much smaller in size than the antennaof the contactless card (see FIG. 1) In the case of a peripheral displaydevice having energy consumption only slightly less than the chip of thecontactless card, the coil may possibly be interlaced or superimposed onthe antenna of the contactless card in order to benefit from bettercoupling.

The screen 16 is preferably a liquid crystal display screen.

FIG. 3 represents the electrical circuit diagram of the contactlesssmart card 30. It is characterized by its coupling antenna 32, at leastone capacitor 33 enabling the card to have a tuning capacitorintervening in the coupling with the reader at the frequency of 13.56MHz. It also includes several resistors, including at least one resistor34 which can be switched with a switch 35 in order to generate aretromodulation frequency between the smart card and the reader.

FIG. 4 represents the electrical circuit diagram of the peripheraldisplay device 36. The latter is characterized by its flat coil 37. Inorder to be able to draw energy from the reader in order to operate theperipheral device, the principle is to use the main resonant circuit ofthe card 30 as the primary of a transformer. The flat coil 37 of theperipheral display device thus forms the secondary of this transformerand receives the energy and the information via electromagneticcoupling. The peripheral display device 36 also includes a resistor 38which is switched by means of a switch 40 and thus modifies theimpedance in order to generate a retromodulation subcarrier frequency.Actually, according to a specific operating mode, the impedance of theperipheral display device can be varied in order to transmit a responseto the reader by means of retromodulation. This response is made bymeans of the contactless smart card's main resonant circuit. Theperipheral display device may also communicate directly with the chip ofthe contactless smart card, depending on the retromodulation format andthe type of retromodulator incorporated in it.

As shown in FIG. 4, the circuit of the peripheral display device 36 doesnot present a tuning capacitor. Thus, it cannot function as a standalonedevice. It must thus benefit from the overvoltage associated with thetuning of the contactless smart card with the reader, via coupling withthe main antenna circuit.

As with all transformers, the impedance presented by the electronics ofthe peripheral display device can be compared to the impedance presentedfrom the chip on the main antenna of the contactless card, on the basisof a coupling mutual surge impedance m between the main antenna and theflat coil and the ratio n1/n2, n1 being the number of turns of thecontactless card's antenna and n2 being the number of turns of theantenna of the peripheral display device.

If the peripheral display device has a strong impedance and a very weakparasite capacitance in front of the rectifier, it may be supplied whenthe contactless card is within the reader's magnetic field, and withoutsignificantly downgrading the latter's operation.

According to an operating mode of the peripheral display device, thelatter exploits the data generated by the contactless card's chip in theform of a specific instruction and emitted by the latter's main antenna.This instruction is generated once the transaction between thecontactless card and the reader is accomplished.

According to another operating mode of said peripheral display device,the latter can exploit data which are dedicated to it and that itreceives from the reader at the time of energy transmission, this databeing transmitted in amplitude modulation to the contactless card, andthen emitted by the card's main antenna.

According to another specific mode, the screen of the peripheral displaydevice maintains an after-image. The information remains displayed onthe screen after the transaction so that the user can see theinformation, up until the next transaction. This long-persistence screenmay consist of a bistable liquid crystal screen. This recently developedtechnology consists in using liquid crystals which have the ability toremain in a certain state without consuming energy. These liquidcrystals only use energy to change their state.

An alternative to using a bistable liquid crystal screen consists inusing a peripheral display device which has at least one storagecapacitor. In order to obtain a persistent image on the liquid crystaldisplay, a sufficient voltage must be applied to the screen's terminalsin order to maintain the liquid crystals in their state. One of thepossibilities is to insert a capacitance into the peripheral displaydevice which charges when the card is in the reader's magnetic field.The energy is transmitted to the capacitor after rectification by theflat coil of the peripheral display device which receives theinformation and the energy. The electric charge stored in thecapacitor(s) is used to supply the screen and to thus maintain theliquid crystals in their state for an above average period of timebetween two passages of the contactless card in the reader's magneticfield.

Another alternative to obtain a persistent display is to use a battery.It is indeed possible to provide the peripheral device with a batterywhich is used to maintain the display. Preferably, a very thin “paperbattery” is used.

Regardless of the means used to obtain a persistent display, therefreshing of the display is obtained exclusively when the contactlesscard is placed in the magnetic field of the reader when the informationpasses between the reader and the contactless card.

The contactless peripheral display device according to the invention canbe integrated into the contactless card during its fabrication; in thiscase it cannot be separated from the card. It can also be affixed to apre-existing contactless card, especially by using adhesive, and thuscan be, in this case, separated from the contactless card.

In the case where the contactless peripheral display device can beseparated from the contactless card, display refreshing is only possibleif it is near the contactless card when it is placed in the magneticfield of the reader. The device according to the invention must beplaced directly on the card or very near it.

The peripheral display device according to the invention thus consistsof a contactless display device which is independent and notelectrically connected to the chip of the contactless card. The interestin the independence of the peripheral display device is that it has noimpact on the functionality of the contactless card nor on thetransactions that are carried out between the card and the reader. Inthis manner, in the case where the peripheral display device isphysically separated from the contactless card, a malfunction of eitherof the two devices has not impact on the other. One simply has to changethe faulty device.

Such a device may be applied to telephone cards which will eventuallybecome contactless. It could also be adapted to toll road payment cardsin the future if they would be able to store money-credit or a number oftoll booth passages in their memory.

What is claimed is:
 1. A peripheral display device for display ofinformation associated with the use of a contactless portable object,comprising at least one chip, a means for receiving energy and saidinformation, said receiving means comprising a flat coil which is notconnected by ohmic contact to said portable object, at least one energystorage means, and a display means, wherein an antenna of said portableobject and the receiving means are capable of acting as the primary andsecondary, respectively, of a transformer when said portable objectreceives energy and information from a reader of said portable objectthrough electromagnetic coupling.
 2. The peripheral display device ofclaim 1, wherein said energy and information transmitted by the antennaof said portable object are generated by said portable object reader. 3.The peripheral display device of claim 1, wherein said informationtransmitted by the antenna of said portable object is generated by thechip of said portable object.
 4. The peripheral display device of claim1, wherein said information transmitted by the antenna of said portableobject are generated by the chip of said portable object.
 5. Theperipheral display device of claim 1, wherein said energy storage meansis a capacitor.
 6. The peripheral display device of claim 1, whereinsaid display means is capable of generating a persistent display, suchthat information remains displayed on said display means for apredetermined period of time.
 7. The peripheral display device of claim6, wherein the long-persistence display means is a bistable liquidcrystal screen.
 8. The peripheral display device of claim 6, wherein thedisplay means is provided with a long-persistence screen feature due toenergy stored in said energy storage means.
 9. The peripheral displaydevice of claim 1, wherein said device is integrated into said portableobject, said flat coil being in the same plane as said antenna of saidportable object.
 10. The peripheral display device of claim 1, whereinsaid device can be separated from said portable object.
 11. Theperipheral display device of claim 1, wherein said device is capable ofsending a response to said portable object reader by retromodulation,via said flat coil, coupled to the antenna of said portable object.